Chondrichthyes is a class of jawed fish that contains the cartilaginous fish or chondrichthyians, which all have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or bony fish, which have skeletons primarily composed of bone tissue. Chondrichthyes are aquatic vertebrates with paired fins, paired nares, placoid scales, conus arteriosus in the heart, and a lack of opecula and swim bladders. Within the infraphylum Gnathostomata, cartilaginous fishes are distinct from all other jawed vertebrates.
Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement, kind, and number of teeth in a given species at a given age. That is, the number, type, and morpho-physiology of the teeth of an animal.
Gnathostomata are the jawed vertebrates. Gnathostome diversity comprises roughly 60,000 species, which accounts for 99% of all living vertebrates, including humans. In addition to opposing jaws, living gnathostomes have true teeth, paired appendages, the elastomeric protein of elastin, and a horizontal semicircular canal of the inner ear, along with physiological and cellular anatomical characters such as the myelin sheaths of neurons, and an adaptive immune system that has the discrete lymphoid organs of spleen and thymus, and uses V(D)J recombination to create antigen recognition sites, rather than using genetic recombination in the variable lymphocyte receptor gene.
Placodermi is a class of armoured prehistoric fish, known from fossils, which lived from the Silurian to the end of the Devonian period. Their head and thorax were covered by articulated armoured plates and the rest of the body was scaled or naked, depending on the species. Placoderms were among the first jawed fish; their jaws likely evolved from the first of their gill arches.
Dorudon ("spear-tooth") is a genus of extinct basilosaurid ancient whales that lived alongside Basilosaurus 40.4 to 33.9 million years ago in the Eocene. It was a small whale, with D. atrox measuring 5 metres (16 ft) long and weighing 1–2.2 metric tons. Dorudon lived in warm seas around the world and fed on small fish and mollusks. Fossils have been found along the former shorelines of the Tethys Sea in present-day Egypt and Pakistan, as well as in the United States, New Zealand and Western Sahara.
Pteraspidomorphi is an extinct class of early jawless fish. They have long been regarded as closely related or even ancestral to jawed vertebrates, but the few characteristics they share with the latter are now considered as basal traits for all vertebrates.
The Bahamas sawshark, Pristiophorus schroederi, is a sawshark of the family Pristiophoridae, found in the western Central Atlantic Ocean from the Bahamas and Cuba at depths of between 400 and 1,000 m. These sharks are at least 80 cm long.
Cyclostomi, often referred to as Cyclostomata, is a group of vertebrates that comprises the living jawless fishes: the lampreys and hagfishes. Both groups have jawless mouths with horny epidermal structures that function as teeth called ceratodontes, and branchial arches that are internally positioned instead of external as in the related jawed fishes. The name Cyclostomi means "round mouths". It was named by Joan Crockford-Beattie.
Stethacanthus is an extinct genus of shark-like holocephalians which lived from the Late Devonian to Late Carboniferous epoch, dying out around 298.9 million years ago. Fossils have been found in Australia, Asia, Europe and North America.
Dromaeosauroides is a genus of dromaeosaurid theropod dinosaur from the Early Cretaceous of what is now Denmark and possibly also England. It was discovered in the Jydegaard Formation in the Robbedale valley, on the island of Bornholm in the Baltic Sea. This is the only likely place for dinosaur remains to be discovered on Danish territory, since the Mesozoic deposits exposed in the rest of the country are marine. Dromaeosauroides is the first known dinosaur from Denmark, and the only one which has been scientifically named. It is one of the oldest known dromaeosaurs in the world, and the first known uncontested dromaeosaur from the Early Cretaceous of Europe.
Hindeodus is an extinct genus of conodonts in the family Anchignathodontidae. The generic name Hindeodus is a tribute to George Jennings Hinde, a British geologist and paleontologist from the 1800s and early 1900s. The suffix -odus typically describes the animal's teeth, essentially making Hindeodus mean Hinde-teeth.
Velociraptorinae is a subfamily of the theropod group Dromaeosauridae. The earliest velociraptorines are probably Nuthetes from the United Kingdom, and possibly Deinonychus from North America. However, several indeterminate velociraptorines have also been discovered, dating to the Kimmeridgian stage, in the Late Jurassic Period. These fossils were discovered in the Langenberg quarry, Oker near Goslar, Germany.
Plesiosuchus is an extinct genus of geosaurine metriorhynchid crocodyliform known from the Late Jurassic of Dorset, England and possibly also Spain. It contains a single species, Plesiosuchus manselii.
Andreolepis is an extinct genus of prehistoric fish, which lived around 420 million years ago. It was described by Walter Gross in 1968 based on scales found in the Hemse Formation in Gotland, Sweden. It is placed in the monogeneric family Andreolepididae and is generally regarded as a primitive member of the class Actinopterygii based on its ganoid scale structure; however some new research regards it as a stem group of osteichthyans.
Phyllodontosuchus is a genus of sphenosuchian, a type of basal crocodylomorph, the clade that comprises the crocodilians and their closest kin. It is known from a skull and jaws from Lower Jurassic rocks of Yunnan, China. Phyllodontosuchus is unusual because some of its teeth were leaf-shaped, like those of some herbivorous dinosaurs, and it does not appear to have been a strict carnivore like most other crocodylomorphs.
A tooth is a hard, calcified structure found in the jaws of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tearing food, for defensive purposes, to intimidate other animals often including their own, or to carry prey or their young. The roots of teeth are covered by gums. Teeth are not made of bone, but rather of multiple tissues of varying density and hardness that originate from the outermost embryonic germ layer, the ectoderm.
Ymeria is an extinct genus of early stem tetrapod from the Devonian of Greenland. Of the two other genera of stem tetrapods from Greenland, Acanthostega and Ichthyostega, Ymeria is most closely related to Ichthyostega, though the single known specimen is smaller, the skull about 10 cm in length. A single interclavicle resembles that of Ichthyostega, an indication Ymeria may have resembled this genus in the post-cranial skeleton.
Ostafrikasaurus is a genus of theropod dinosaur from the Late Jurassic period of what is now Lindi Region, Tanzania. It is known only from fossil teeth discovered sometime between 1909 and 1912, during an expedition to the Tendaguru Formation by the Natural History Museum of Berlin. Eight teeth were originally attributed to the dubious dinosaur genus Labrosaurus, and later to Ceratosaurus, both known from the North American Morrison Formation. Subsequent studies attributed two of these teeth to a spinosaurid dinosaur, and in 2012, Ostafrikasaurus crassiserratus was named by French palaeontologist Eric Buffetaut, with one tooth as the holotype, and the other referred to the same species. The generic name comes from the German word for German East Africa, the former name of the colony in which the fossils were found, while the specific name comes from the Latin words for "thick" and "serrated", in reference to the form of the animal's teeth.
Romundina is a small, heavily armored extinct genus of acanthothoracid placoderms which lived in shallow marine environments in the early Devonian (Lochkovian). The name Romundina honors Canadian geologist and paleontologist Dr. Rómundur (Raymond) Thorsteinsson of Calgary, Alberta, Canada. Romundina are believed to have lived on Earth between 400 and 419 million years ago. The closest known relative to Romundina is the acanthothoracid Radotina. The type and only described species is R. stellina.
Andersonerpeton is an extinct genus of aïstopod from the Bashkirian of Nova Scotia, Canada. It is known from a single jaw, which shares an unusual combination of features from both other aistopods and from stem-tetrapod tetrapodomorph fish. As a result, Andersonerpeton is significant for supporting a new classification scheme which states that aistopods evolved much earlier than previously expected. The genus contains a single species, A. longidentatum, which was previously believed to have been a species of the microsaur Hylerpeton.
